Field
The present disclosure relates to a printed circuit board having an EMI shielding function and a method for manufacturing the same, and more particularly to a printed circuit board having an EMI shielding function and a method for manufacturing the same, which can inhibit EMI among a plurality of neighboring signal units.
Description of the Related Art
In general, a flexible printed circuit board (FPCB) is fabricated using a kind of printed circuit technique and is generally used for electrically connecting a rigid printed circuit board (PCB) to another rigid PCB.
The FPCB is generally configured to have a single surfaced structure or a double surfaced structure. The conventional FPCB has been typically used simply for connecting circuits to each other.
When an electrical signal is applied to the FPCB, electromagnetic wave interference (EMI) is generated. The EMI is harmful to human body and generates noises from products employing the FPCB, which is a major cause of quality defects. Accordingly, various methods for avoiding such a problem are being attempted. One of the attempted methods is to employ an EMI shielding film to the FPCB.
FIGS. 1A and 1B illustrate a conventional flexible printed circuit board (FPCB) with an EMI shielding film. Specifically, FIG. 1A is a plan view of the conventional FPCB and FIG. 1B is a cross-sectional view taken along the line A-A′ of FIG. 1A.
As illustrated in FIGS. 1A and 1B, the conventional FPCB includes signal lines 14D and ground lines 14G formed on a base film 12, a resin layer 16 provided on the signal lines 14D and the ground lines 14G, and an EMI shielding film 1 disposed on the resin layer 16.
Here, the signal lines 14D are conductive paths for data signal transmission and the ground lines 14G are conductive paths for grounding.
The EMI shielding film 1 includes a polymeric cover film 1a, a conductor layer 1b formed on the coverfilm 1a as a thin metal layer, and a conductive adhesive layer 1c widely coated on one surface of the conductor layer 1b and made of an adhesive resin. The conductive adhesive layer 1c is formed by mixing a conductive metal with a general resin. Silver, nickel or copper may be used as the conductive metal.
In order to allow the EMI shielding film 1 to exert an EMI shielding effect, it is necessary to electrically connect the conductor layer 1b to the ground lines 14G using the conductive adhesive layer 1c. However, since the conductive adhesive layer 1c is hardened when heat and pressure are applied thereto, flexibility of the FPCB may be lowered.
In addition, the EMI generated from the signals lines 14D provided on the base film 12 may interfere with the EMI generated from neighboring signal lines 14D, undesirably generating noises. Particularly, the longer the FPCB, the more the noises generated. In addition, the higher the frequencies of signals passing the signal lines 14D, the more the noises generated. Therefore, high-capacity data, such as high-definition video images, cannot be transmitted at a high speed using a long FPCB.